A child psychologist held back tears as she told a royal commission how her son was allegedly abused by a teacher at the private school she believed to be "nurturing and protective".
Marija Radojevic told the Royal Commission into Institutional Responses to Child Sexual Abuse she trusted the school implicitly.
The commission is hearing evidence into how sexual predators manipulate their victims as well as those around them.
"My husband and I had no reason to suspect that our son was being groomed by an unmarried teacher," she said.
"We did not know it was happening right under our nose. We truly believed that the Christian ethic with which our son was raised and which the school espoused was a nurturing and protective one."
Dr Radojevic told the commission she and her husband, a child psychiatrist, placed too much trust in the unnamed school.
"To this extent we had become entrapped," she said.
Under questioning from Dr Radojevic, her son named the teacher. Her son died in 2014, after suffering an epileptic fit.
"We are now left to deal not only with our endless feelings of loss and trauma but also with the deep guilt about our naive ignorance," she said.
Another witness, given the pseudonym CAA, told the commission how an older predator manipulated him by telling him sexual contact was, "Good for me and necessary to my development as a person."
Now 28, he told the inquiry the secrecy and stigma associated with sexual abuse makes it harder for people to come forward.
"This is one of the jarring features of the phenomenon of sexual abuse - it is so widespread and at the same time so unknown," he said.
The commission heard perpetrators can groom entire organisations, gaining the support of supervisors and colleagues to disguise their motivations.
Katherine Levi, chief executive of abuse prevention body Child Wise, said many groups lacked appropriate procedures to screen and supervise staff and volunteers.
"The lack of resources create conditions that make organisations more vulnerable to accepting perpetrators within their ranks unknowingly," she said
Relying on screening mechanisms could lead to complacency, the commission heard.
"One of the problems in Australia is our over reliance on working with children checks," Ms Levi said.
"If you haven't had a criminal charge in the past, you are fit to work with children and therefore beyond suspicion."
Irish academic Anne-Marie McAlinden's research cites the quote, "monsters do not get children, nice men do" to illustrate misconceptions about offenders.
"The focus on the predatory stranger, that does society a disservice," she said.
The hearing into the cause, nature and impact of child sexual abuse before Justice Peter McClellan, continues.
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